ENH: Remove unused variable and commented code block

Remove unused variable and commented code block: getting the largest
possible region of the superclass (`ImageToImageFilter`) is most likely
being exercised in ITK proper.

Fixes:
```
test/itkMorphologicalContourInterpolationTest.cxx:37:34:
 warning: unused variable 'reg' [-Wunused-variable]
   37 |   typename ImageType::RegionType reg = test->GetLargestPossibleRegion();
      |                                  ^~~
```

raised for example in:
https://open.cdash.org/viewBuildError.php?type=1&buildid=10154304

test/itkMorphologicalContourInterpolationTest.cxx

@@ -33,14 +33,6 @@ doTest( std::string inFilename, std::string outFilename, bool UseDistanceTransfo
 
   typename ImageType::Pointer test = reader->GetOutput();
 
-  // region for partial coverage
-  typename ImageType::RegionType reg = test->GetLargestPossibleRegion();
-  // for (int i = 0; i < ImageType::ImageDimension; i++)
-  //  {
-  //  reg.GetModifiableIndex()[i] += (reg.GetSize(i) - 1) / 4;
-  //  reg.SetSize(i, (reg.GetSize(i) + 1) / 2);
-  //  }
-
   using mciType = itk::MorphologicalContourInterpolator< ImageType >;
   typename mciType::Pointer mci = mciType::New();
   mci->SetInput( test );